This invention relates to the synthesization of sound and more particularly to a speech synthesizer using phonetic sounds.
The increased use of computers combined with telephone links has created a need for automated speech synthesizers. The use of automated speech provides a vehicle for the establishment of low cost transmission of the computed or retrieved data to a user at a distant location. To date, automated speech systems stored spoken words in memory, and upon activation by the external computer, the words are released, either singly, or in combination.
While this method produces and transmits the spoken word over a telephone line, this technique is limited in size and cost, since the vocabulary is limited by the number of word cells that can be economically stored in memory. In comparison, it may be compared to a typewriter that is arranged with a keyboard of words rather than letters. Such an arrangement would be obviously limited.
The use of automated speech synthesizers is not new, and a number of techniques have been developed to implement speech synthesizers. One such system was developed using optical sound tracks upon a drum, with the desired track selected by enabling a photo pickup adjacent to the desired sound track. Each revolution of the drum provided a sound recording time duration of one word length. The number of words that could thus be contained was equal to the number of sound tracks (rings) axially placed upon the drum.
In another arrangement musical sounds and phrases were placed upon a series of 36 separate tapes. The desired tape was thus selected and pulled over the read head on the respective track. Upon cessation of the sound, the tape was immediately restored to the initial position thus readying it for reuse. While the sound quality was very good, the reliability of this device was relatively low, and the tapes would eventually wear out.
In another arrangement an integrated circuit type memory speech reproducing system was developed with each memory element containing one spoken word (about one second of audible storage).
Synthesized speech systems have been developed over the past two decades, including vocoder type systems for speech digitization. These devices are costly, and often sound very metallic, providing a relatively poor reconstruction of vocal sounds.